• android ViewPager中页面延迟加载的实现


    对于viewpager的使用,如果说是请求的数据对内存的消耗不到的话,这是很理想的,但是如果说请求的数据对内存消耗的比较大的话这样就容易出现oom(比如说图片),在使用viewPager的时候使用setOffscreenPageLimit(int size)默认的是1,所以说我们怎么设置这个值,在加载数据的话会将当前页面和下个页面的数据同时的进行请求,这在某种情况下时非常的影响性能的,还有就是在当前页面和下个页面在viewPager中算作了同一个页面,因为你是无法通过生命周期来进行控制数据的延迟加载,所以现在很多网友通过修改v4包进行修改setOffscreenPageLimit(int size)的默认值为0;但是这样虽然效果实现了,但是会引发另一个问题,那就是在切换页面时,中间过渡的是一个大大的黑屏,myGod的这种修改对体验算是致命的打击对于我而言,不过最后终于还是被我搞定了;

     之前的一种方式在我之前的博客中有写,下面介绍的是另一种方式:结合Fragment来处理,废话不说直接上代码:

    MainActivity 
    public
    class MainActivity extends FragmentActivity { private ViewPager pager; private ArrayList<Fragment> fts = new ArrayList<Fragment>(); private String[] urls = new String[]{ "http://t2.qpic.cn/mblogpic/d5149f8549e394000aa6/2000", "http://t2.qpic.cn/mblogpic/fad173ab259d7efbfecc/2000", "http://t2.qpic.cn/mblogpic/463b55016d51d4b9c172/2000", "http://t2.qpic.cn/mblogpic/ab3f96d6095ec82e6d40/2000", "http://t2.qpic.cn/mblogpic/e61f017bcad2684e79f2/2000", "http://t2.qpic.cn/mblogpic/d271142c68e6e1d5b8de/2000", "http://t2.qpic.cn/mblogpic/ef50986bdf4dd8801060/2000", "http://t2.qpic.cn/mblogpic/71585d34aaa60b9dcc2a/2000", "http://t2.qpic.cn/mblogpic/e0011bad45ae23889216/2000", "http://t2.qpic.cn/mblogpic/6e84cb60bf0e6b4945f6/2000", "http://t2.qpic.cn/mblogpic/5a9217624c130c2fa9f8/2000", "http://t2.qpic.cn/mblogpic/7ddb0e9618754fc4bc8e/2000", "http://t2.qpic.cn/mblogpic/eed45f9d4b5001a04b30/2000", "http://t2.qpic.cn/mblogpic/62353a0dbdd40bc1be9a/2000", "http://t2.qpic.cn/mblogpic/0ccf7f16318331e9a892/2000", "http://t2.qpic.cn/mblogpic/4e55efffef93f6d4a86e/2000", "http://t2.qpic.cn/mblogpic/4ac76f1427e4278b7172/2000", "http://t2.qpic.cn/mblogpic/0db3a5a1047d7ee52bdc/2000", "http://t2.qpic.cn/mblogpic/c65d09035d7b6c644d6a/2000", "http://t2.qpic.cn/mblogpic/7ebf4b49bf7e2ef6a716/2000", "http://t2.qpic.cn/mblogpic/4ba5fd867149273f9b02/2000", "http://t2.qpic.cn/mblogpic/4f375f19fbd08151d0f8/2000", "http://t2.qpic.cn/mblogpic/1c22a0574274d0e3c866/2000", "http://t2.qpic.cn/mblogpic/50cdf4f63120ccf74e86/2000", "http://t2.qpic.cn/mblogpic/ab8588008e7865927d7c/2000", "http://t2.qpic.cn/mblogpic/1e9e65d61d5f2bb8ebc4/2000", "http://t2.qpic.cn/mblogpic/6913e7ad5c7267969d9a/2000", "http://t2.qpic.cn/mblogpic/54157580cc7ddf7b2870/2000", "http://t2.qpic.cn/mblogpic/0bd2f9be53d2c9aec8ca/2000", "http://t2.qpic.cn/mblogpic/2041a03d63cc6c5b9b92/2000", }; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); pager = (ViewPager) findViewById(R.id.pager); for (int i = 0; i < urls.length; i++) { fts.add(PhotoFragment.instance(urls[i], i)); } pager.setAdapter(new MyPagerAdapter(getSupportFragmentManager(), fts)); pager.setOffscreenPageLimit(fts.size()); pager.setCurrentItem(0); } private class MyPagerAdapter extends FragmentPagerAdapter{ private ArrayList<Fragment> list; public MyPagerAdapter(FragmentManager fm,ArrayList<Fragment> list) { super(fm); this.list = list; } @Override public Fragment getItem(int arg0) { return list.get(arg0); } @Override public int getCount() { return list.size(); } } }

    PhotoFragment:

    package com.zhizhi.viewpagernocache;
    
    import com.nostra13.universalimageloader.core.ImageLoader;
    
    import android.os.Bundle;
    import android.support.annotation.Nullable;
    import android.support.v4.app.Fragment;
    import android.util.Log;
    import android.view.LayoutInflater;
    import android.view.View;
    import android.view.ViewGroup;
    import android.widget.ImageView;
    
    public class PhotoFragment extends Fragment {
    
        private final static String TAG = PhotoFragment.class.getName();
        private String url;
        private int index;
        private ImageView image;
    
        public static PhotoFragment instance(String url, int index) {
            PhotoFragment fragment = new PhotoFragment();
            Bundle bundle = new Bundle();
            bundle.putString("url", url);
            bundle.putInt("index", index);
            fragment.setArguments(bundle);
            return fragment;
        }
        
        
        
        @Override
        public void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
            if (getArguments() != null) {
                url = getArguments().getString("url");
                index = getArguments().getInt("index");
            }
            setRetainInstance(true);
            
        }
    
        @Override
        public void onSaveInstanceState(Bundle outState) {
            super.onSaveInstanceState(outState);
            outState.putString("url", url);
            outState.putInt("index", index);
            
        }
    
        @Override
        public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
            if (savedInstanceState != null) {
                url = savedInstanceState.getString("url");
                index = savedInstanceState.getInt("index");
            }
            View view = inflater.inflate(R.layout.view_photo, container, false);
            image = (ImageView) view.findViewById(R.id.image);
            return view;
        }
    
        @Override
        public void onActivityCreated(@Nullable Bundle savedInstanceState) {
            super.onActivityCreated(savedInstanceState);
            
        }
    
        @Override
        public void setUserVisibleHint(boolean isVisibleToUser) {
            super.setUserVisibleHint(isVisibleToUser);
            if (isVisibleToUser) {
                Log.i(TAG, "get pic data for show");
                ImageLoader.getInstance().displayImage(url, image);
            }    
        }
    
    }

    以上就是代码的核心部分了;

    源码Demo :https://files.cnblogs.com/kingfly13/ViewPagerNoCache.zip

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  • 原文地址:https://www.cnblogs.com/kingfly13/p/3906738.html
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